Referral bias in aneurysmal subarachnoid hemorrhage

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✓ The objective of this study was to assess the effect of referral bias on survival in patients with subarachnoid hemorrhage (SAH). The characteristics of 49 patients with aneurysmal SAH from a single community were compared with those of 328 patients referred from outside the community, all treated in the same medical care setting. In addition, referral patients who received surgery were compared by differential survival analysis with those still awaiting surgery at Days 1 to 3, Days 4 to 10, and Days 11 to 15.

There was a dramatic difference in the 30-day survival rate between referral patients (83%) and community patients (59%), but most of the difference had occurred by the 2nd day after SAH. In the referral patients, the variables present at first medical attention that were found to have an independent effect on survival were clinical grade, presence of coma, number of days from SAH to referral, diastolic blood pressure, and patient age. There was a higher survival rate at 1 year for patients who were surgically treated compared with those awaiting surgery for each of the three time periods. Patients who underwent early surgical treatment had a 1-year survival rate almost identical to that of patients with late surgery.

Referral patients had a better early survival rate than did community patients because the referral group did not include patients who died and some who were in poor clinical condition before the opportunity for referral. The differential survival analysis described provides a new method for estimating survival for treated and untreated patients with SAH.

Article Information

Address reprint requests to: Jack P. Whisnant, M.D., Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905.

© AANS, except where prohibited by US copyright law.

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Figures

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    Graphs showing the probability of survival for 5 years (left) and for the first 120 hours (right) after the onset of first aneurysmal subarachnoid hemorrhage (SAH) in referral patients and in community patients (n = number of patients).

  • View in gallery

    Graph demonstrating the probability of survival for 5 years after the onset of first aneurysmal subarachnoid hemorrhage (SAH) in patients with clinical Grades I to III in the referral group and in the community group (n = number of patients).

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    Graphs showing the probability of survival for 30 days for patients who had definitive aneurysm surgery compared with that for patients awaiting surgery at specified times after first medical attention for subarachnoid hemorrhage: surgery performed 1 to 3 days (left); 4 to 10 days (center); and 11 to 15 days (right). Patients with clinical Grade V were excluded.

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